1. Field of the Invention
This invention relates generally to fiber lasers and amplifiers. More specifically, it pertains to fiber optical isolators, which are used at high operating power in applications such as high power fiber lasers and amplifiers.
2. Discussion of the Related Art
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Optical isolators typically transmit light in the forward direction with relatively low insertion loss (typically <10% loss), however, backward propagating light may be attenuated by a factor of 1000 to 1,000,000, depending on the design of the isolator. For this reason, optical isolators are often used in fiber lasers and amplifiers to eliminate back reflections, because backward propagating light can damage optical components in the fiber laser and/or amplifier. Furthermore, backward propagating light passing through a gain medium is amplified such that it is more likely to damage components and may cause the laser or amplifier to become unstable.
To reduce the effect of backward light propagation, optical isolators can be placed between amplifier stages or at the output of an amplifier to block back reflections. Conventional optical isolators, however, are limited in their power tolerance. The highest power optical isolators currently available publicly are rated for power between 1 and 2 watts (“W”). This level of power tolerance simply may not be adequate for fiber amplifiers, which can have output powers as high as tens of watts. Isolators that could be used at higher power would be advantageous for higher power fiber amplifiers and lasers because it would enable the isolator to be placed at the output of the amplifier where it could provide greater protection against back reflections.